1. Field of the Invention
The present invention relates to a zoom motor control for use in combination with an auto zoom device of a movie camera and more particularly to a zoom motor control which incorporates a strain gauge sensor and which an operator, who controls the auto zoom device by pressing the strain gauge sensor with his thumb, has sensitive tactile feedback and therefore substantially better control over the auto zoom device.
2. Background of the Prior Art
U.S. Pat. No. 3,834,796, entitled "Auto Zoom Device for a Motion Picture Camera", issued to Yoshio Komine on September 10, 1974, teaches an auto zoom device for a motion picture camera wherein the zoom motor control can make a changeover from auto zoom by an electric motor to manual zoom. The auto zoom device includes a engaging-disengaging mechanism which is disposed between a rotating member and a zoom lens rotating tube member. An electric motor drives the rotating member which in turn drives the zoom lens rotating tube member. A change-over member permits a changeover between auto zoom and manual zoom. A rotating lever shifts the engaging-disengaging mechanism between operative and inoperative positions in an interlocking relationship with the change-over member. A quick zoom-up operating mechanism is cooperable with the rotating lever independently of the changeover member thereby permitting quick zoom-up in either state, auto zoom or manual zoom.
A description of a 12-V/dc servo zoom drive motor appears in the Journal of the Society of Motion Picture and Television Engineers, Volume 87, October 1978, page 742. The control for the servo motor is in the form of a grip which can be attached to the camera or to a tripod handle. The upper cone-shaped section of the grip has a thumb recess that rotates in order to control zoom-in, zoom-out and zoom speed. The servo system senses variations in the mechanical load and electrical power and automatically compensates. A separate control on the grip pre-establishes maximum zoom speed wherein an operator can predetermine the fastest speed needed for the zoom and concentrate on the smooth "feathering" of the effect. The drive motor operates from 12 volt, direct current power supplies.
Cinema Products Corporation has published on Dec. 1, 1981 a second edition of its technical manual entitled J-4 Zoom Control and Motor, in which there is a description of a J-4 Zoom Control System which is used to control zoom functions of cinema lenses. The J-4 Zoom Control System includes a joystick control, an electronic control box and a J-4 silent servo motor. The joystick control may be held in the hand or attached to the handle of the tripod. The joystick thumbwheel controls the direction and speed of the zoom. The maximum speed of the zoom is controlled by a knob on the electronic control box. The speed range of the joystick may therefore be very wide or intentionally limited as the situation dictates. The thumbwheel also controls power to the electronic control box and its use conserves battery power and eliminates a separate on/off switch. The J-4 silent servo motor includes a tachometer.
The J-4 Zoom Control System requires mechanical adjustment to the joystick control and it is difficult to obtain a smooth zoom of the lens of the movie camera.